One can use "pencil" ✏️ to make notes regarding assumed numbers in cells. Once the decision is made, one should put a final number into the cell instead of a 'note'.

How to use:

1. tap the pencil icon;
2. put an assumed number into a cell;
3. as soon as you are sure, which number to put into the cell, just place a 'normal' number instead of the 'note'.